1. Field of the Invention
The present invention relates to the field of toners or inks used in imaging processes, particularly electrophotographic or electrographic imaging processes. The invention also relates to compositions, apparatus and methods for reducing solvent or carrier emission in imaging systems.
2. Background of the Art
Electrophotography is generally classified into wet and dry methods. In the former, a permanent image may be obtained through the steps of forming an electrostatic latent image on an image-bearing element such as a selenium electrophotographic element, a zinc oxide electrophotographic element or the like, developing the thus formed image with a liquid developer, transferring the developed image onto a transfer sheet as occasion demands, and thereafter heating and drying the developed or transferred image by means of a heating means such as heat roller or the like further as occasion demands. In the latter, on the other hand, a permanent image may be obtained through the steps of developing an electrostatic latent image formed in the same manner as described above with a powder developer (toner particles), transferring said image onto a transfer sheet as occasion demands, and thereafter thermally fixing the image by means of a heating means such as heat roller or the like. In addition, a method is also known which is designed to form an electrostatic latent image on an electrostatic recording element (which is also called a dielectric element) in place of an electrophotographic element. In this connection, it is to be noted that the electrophotographic element and electrostatic recording element shall hereinafter be called “an element being developed” respectively.
In the case of the wet method, an odorous solvent vapor-containing exhaust gas is discharged from a wet type electrophotographic machine utilizing this method, because the liquid developer used in the developing step contains a large quantity of solvent consisting essentially of a hydrocarbon, such as a paraffinic or isoparaffinic hydrocarbon. This solvent vapor is caused by evaporation of the solvent attached to the element being developed in the developing step or to the transfer member in the transferring step, but additionally by evaporation of the solvent attached to the developing unit or the like. This generation of solvent vapor is further accelerated when the element being developed or transfer member is heated and dried in a drying step and/or is fused to permanently fix the image to a final receptor by means of a heating means. Even in “dry” toner systems, there is residual solvent (also usually non-polar hydrocarbon solvent) present in the toner that is released by development procedures.
Usually, such a solvent vapor-containing exhaust gas has been discharged to the outside of a machine without undergoing any treatment. Due to this, it has been called into question from the standpoint of environment sanitation that a small, especially confined room is filled with a high concentration of solvent gas in a short time in the cases of operating a machine at a high speed even when ventilating the room as well as operating the machine without ventilating the room. Therefore, various schemes to improve this problem have hitherto been proposed, for instance, (1) the use of a reversing squeeze roller for reducing the quantity of solvent attached to an element being developed and thereby suppressing the quantity of solvent vapor generated in the exhaust gas (which is disclosed, for instance, in U.S. Pat. No. 3,907,423 or German Pat. No. 2,361,833), (2) the introduction of exhaust gas (which has been collected by means of an air duct, this being applicable to the exhaust gas appearing hereinafter) to an adsorbent layer for allowing the gas to adsorb the solvent vapor, (3) the introduction of the exhaust gas into a high boiling solvent likewise for allowing said gas to adsorb the solvent vapor, (4) the passage of the exhaust gas through a condenser for removing a liquidified solvent vapor therefrom (which is disclosed, for instance, in U.S. Pat. No. 3,130,079), (5) the conversion of the solvent vapor contained in exhaust gas into a different substance through the reaction thereof with a reactive substance, and so forth. However, the scheme (1) still involves problems to be solved in image quality, that is, the resulting copy is of deteriorated image density and further the wide image area lacks the uniformity of image, the scheme (2) is defective in that the efficiency of adsorption is low, the scheme (3) is defective in that the efficiency of adsorption is more inferior than that of the scheme (2), the scheme (4) is defective in that the apparatus therefor becomes complicated and large-sized, which leads to high cost, and the scheme (5) has a problem to be solved in that a different odorous substance is created.
In the case of the dry method, on the other hand, an odorous gas is exhausted from an electrophotographic machine, too. The odorous substances contained in this exhaust gas, which are caused when the toner used is thermally fixed, are different in composition from those of the exhaust gas from the wet type electrophotographic machine, and in more detail comprise those generated from the toner particles and the electrophotographic element-constituting materials (various kinds of resins), for instance, such as the residual solvent, unreacted monomer and its decomposition gas and remaining solvent contained in the material resins and additionally those generated from the material constituting the surface of the heat roller (silicone resin), for instance, such as the remaining polymerization catalyst, silicone oil and the like. In either case, it is noted that these odorous substances are generated in a marked degree when using high-speed electrophotographic machines, in particular those wherein flash fixing is employed. To reduce these emissions, techniques such as condensation of the vapor or catalytic conversion of the vapor have been used.
U.S. Published Patent Application 2004/0146314 describes an exhaust system of a liquid electrophotography printer comprising an exhaust line to discharge air inside an engine cell to an outside thereof; at least one exhaust fan, which is installed inside the exhaust line to generate and move the air inside the engine cell; a heating coil to heat the air to be discharged through the exhaust line to ignite impurities contained in the air; and an oxidative catalyst filter to filter and deodorize the impurities.
For example, U.S. Pat. No. 4,415,533 (Kurotori et al.) discloses a process and apparatus for treating exhaust gas from an electrophotographic machine. The odorous exhaust gas is oxidized, in the presence of a heated oxidation catalyst, to make the exhaust gas odorless. The catalyst must be heated so that it may be activated. As the heating system for the catalyst, there may be employed any one of the inside and outside heating systems. It goes without saying that the process according to the present invention is applicable to electrophotographic machines not only having a drying or heat fixing unit but also lacking a drying or heat fixing unit. In case where this machine is a wet type electrophotographic machine, it is preferable that at least a part of the heat for use in heating the catalyst should be utilized for the purpose of drying a copy material leaving the machine because said copy material is still remaining wet. These catalysts, when used, are carried on normal carriers such as alumina, silica, diatom earth, clay and the like. With reference to the configuration of catalysts there is no specific limitation, but the catalysts used are normally of a honey-comb construction.
U.S. Pat. No. 5,198,195 describes a developer treatment apparatus for treating excess developer after development of a film in a development chamber with the developer which contains a solvent composed of a hydrocarbon as a main component and a pigment dispersed in the solvent, the improvement of said developer treatment apparatus comprising: a tank for receiving excess developer, the tank having an opening for receiving an inflow of the excess developer exhausted from the development chamber. There is a passage connected between the development chamber and the tank opening through which excess developer is supplied to the tank after development in the development chamber. A catalyst for oxidizing excess developer received in the tank by converting excess developer into gases made of water vapor and carbon dioxide and discharging the gases. There is a vaporization means for vaporizing excess developer received in the tank and for supplying vapor of the excess developer to the catalyst. There is a catalyst igniting heater for first oxidizing said vaporized excess developer and a system for intermittently supplying new developer to the development chamber. There is also means for supplying electricity to the catalyst igniting heater after the new developer, which has been supplied to the development chamber by the developer supplying means, flows into the tank through the passage and the tank opening, such that the vapor of the excess developer is spontaneously combustible even when the development treatment apparatus, the vaporization means and the catalyst igniting heater are turned off.
A difficulty in the use of this type of catalytic reduction system relates to the fact that the catalyst must be heated (e.g., at least 150 to 400C) to enable decomposition of the carrier vapor, and that the catalyst must be hot when the vapor reaches the catalyst to be effective. If there is a significant delay in the heating, some vapor will pass through the catalytic converting area without being decomposed. It has therefore been suggested that the catalyst be maintained at a high temperature in expectation of the passage of the carrier vapor. This is both expensive (because of energy consumption) and potentially dangerous (by maintaining a very hot element within the machine).